1. Field of the Invention
The present invention relates to a control device for an antilock brake system, and more particularly to a control device for an antilock brake system in which braking hydraulic pressure is controlled by a turning angle of a servomotor.
2. Background Art
An antilock brake system (ABS) for performing optimum brake control has been mounted on conventional vehicles. In the ABS, a slip rate is calculated from the rotation speed of a wheel of the running vehicle and the vehicle velocity, and the optimum brake control is performed based on the calculated slip rate.
In an ABS according to the conventional art, as disclosed in Japanese Pre-examination Patent Publication (KOKAI) No.Hei 5-79543 (1993), an actuator for an antilock brake for reducing, maintaining and increasing the braking hydraulic pressure is connected between a master cylinder and a caliper cylinder. The master cylinder is responsible for converting a brake operation to hydraulic pressure. The actuator incorporates a servomotor for displacing a crankshaft of the actuator based on slip rate information of the vehicle, and the crankshaft opens and closes a cut valve through an expander piston, thereby controlling the braking hydraulic pressure applied to the caliper cylinder.
Stopper members are preliminarily provided at an upper limit position and a lower limit position of a turning range of the crankshaft. When the upper limit position or the lower limit position is given as a target angle to the servomotor, the crankshaft or a member in the vicinity of the crankshaft is turned until a positioning member provided in the vicinity of the crankshaft/member comes to collide with the stopper member.
However, in the conventional art as mentioned hereinabove, the positioning member collides against the stopper member at a high speed when a target position for the servomotor is set at either the upper limit position or the lower limit position. Therefore, the positioning member and the stopper members must be provided with sufficient mechanical strength. This structural requirement further hinders size reduction and weight reduction attempts of the designer of an actuator.
The present invention overcomes the shortcomings associated with the related art and achieves other advantages not realized by the related art.
It is an aspect of the present invention to provide a control device for an antilock brake system which solves the above-mentioned problems in the prior art.
It is an aspect of the present invention to provide a control device that permits an actuator to be reduced in size and weight by moderating the collision of a positioning member against a stopper member.
These and other aspects of the invention are accomplished by a control device for an antilock brake system comprising an input hydraulic chamber in communication with a master cylinder, an output hydraulic chamber in communication with a caliper cylinder of a brake, a cut valve in communication with the input hydraulic chamber and the output hydraulic chamber for providing a hydraulic cutoff condition, an expander piston for opening the cut valve, wherein the expander piston is located on an open end side of the cut valve in an open position, and the expander piston closes the cut valve by increasing a volume of the output hydraulic chamber in a closed position, wherein the expander position is located in a closed end side in the closed position, a crank mechanism for displacing said expander piston, a servomotor for turning said crank mechanism to a predetermined target angle, and a stopper member for setting a turning limit for said crank mechanism, said expander piston is displaced in a step of reaching said closed position during an ABS operation and being retracted to said open position during a non-ABS operation.
These and other aspects of the invention are accomplished by a control device for an antilock brake system comprising an input hydraulic chamber in communication with a master cylinder, an output hydraulic chamber in communication with a caliper cylinder of a brake, a cut valve in communication with said input hydraulic chamber and said output hydraulic chamber for providing a hydraulic cutoff condition, an expander piston for opening said cut valve, wherein said expander piston is located on an open end side of said cut valve in an open position, and said expander piston closes said cut valve by increasing a volume of said output hydraulic chamber in a closed position, wherein said expander position is located in a closed end side in said closed position, a return control for retracting the expander piston to said open and closed positions, the return control includes means for executing a first control procedure for driving the servomotor with a position precedent and a target angle to the turning limit, and means for executing a second control procedure for driving the servomotor by updating the target angle with the turning limit, a crank mechanism for displacing the expander piston, a servomotor for turning the crank mechanism to a predetermined target angle, and a stopper member for setting a turning limit for the crank mechanism, the expander piston is displaced in a step of reaching the closed position during an ABS operation and being retracted to the open position during a non-ABS operation.
According to the above description, a position precedent to the turning limit is first set as a turning target angle for the crank mechanism, so that the turning speed of the crank mechanism is only reduced at the position precedent to the turning limit. The target angle is then updated and the crank mechanism is again turned to the turning limit. Accordingly, the kinetic energy of the crank mechanism at the time of reaching the turning limit is smaller as compared with the case where the turning limit is set as the target angle from the beginning. The kinetic energy of the crank mechanism at the time of collision with the stopper member at the turning limit is advantageously reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.